The invention relates to press-loading energetic material into warhead projectiles.
A conventional press-loading process for a projectile uses multiple increments of powder to achieve specified quality requirements. Warhead projectiles typically are shaped with a length-to-diameter (l/d) ratio that balances ballistics and payload. When press-loading projectiles with larger l/d ratios, quality and performance issues arise due to an inherent inefficiency in pressing long charges of powder. It is known that friction forces, both inter-particle and wall-boundary, are quality factors that must be minimized during the press-loading process. Otherwise, the pressed charge will have a density gradient marked by significant degradation along its central axis and further from the press punch. Consequently, long powder charges cannot be pressed to meet density and mass specifications. The conventional pressing process relies on multiple pressed increments of powder to reduce the l/d ratio to a manageable amount.
Conventional load procedures typically require that multiple increments of powder or pre-consolidated pellets are loaded and compacted individually. For example, for a cylindrical die, efficient consolidation of energetic material is only achieved if the punch diameter is equal to or greater than the length of the container (l/d less than 1). Thus, in the conventional process, the powder is poured and pressed incrementally. Inefficient cohesion between subsequent compacted layers and sharp corners left behind upon withdrawal of the punch may cause the layers to crack and de-laminate internally. Poorly bonded layers and low-density areas manifest themselves as transverse cracks and internal voids. When a warhead is launched, the case is propelled forward while the energetic fill is forced against the back of the case under its own momentum. This phase, referred to as setback acceleration, harbors severe risk of unintended initiation as any transverse cracks in the energetic material may close violently. Conversely, with particularly insensitive compositions, a warhead may not reliably initiate if a detonation wave cannot cross these large transverse voids.
To obtain consistent quality through the entire length of a column of energetic material, each pressed increment requires a complete cycling of all the pressing steps and parameters including loading, vacuum dwell, pressure dwell, pressure cycling, and unloading. Generally, the use of fewer increments reduces the total cycle time but decreases the overall quality. A balanced process can be achieved, but throughput in a production setting is always choked by incremental press-loading.
A need exists for a faster method of press-loading energetic material that results in consistently high quality throughout the column of energetic material.